1. Field of the Invention
The invention concerns an intumescent, fire retardant material that has the ability to remain in an unexpanded elastomeric form until heat produced by a fire causes it to expand to fill burned-out voids with a fire-resistant barrier. The invention is particularly concerned with intumescent, fire retardant material that is water-based and caulkable.
2. Description of the Related Art
U.S. Pat. No. 4,273,879 (Langer et al.) discloses flexible, intumescent, fire retardant materials that can range from a soft putty-like consistency to a hard rubber. Useful materials can be compounded to include an intumescent component such as hydrated alkali metal silicate granules, an organic binder component such as polychloroprene, an organic char-forming component such as a phenolic resin, and fillers such as silica. If any of the intumescent granules of the examples of the Langer patent were to be immersed in water for long periods of time, the alkali metal would gradually be leached away from the silicate granules, thus reducing their ability to intumesce. In answer to this problem, U.S. Pat. No. 4,218,502 (Graham et al.) applies to the hydrated alkali metal silicate granules a protective moisture-resistant coating such as a metal salt of a long-chain fatty acid.
U.S. Pat. No. 4,234,639 (Graham) further improves intumescent hydrated silicate particles such as those of Graham et al. '502 by coating the granules with a mixture of a halogenated organic compound and an iron-containing compound. When the particles are incorporated into asphalt shingles and exposed to fire, the coating presumably can catalyze the charring of the asphalt.
Like Graham '639, U.S. Pat. No. 4,521,333 (Graham et al.) is also directed to the problem that water is known to leach away the alkali metal from hydrated alkali metal silicate granules. Graham et al. '333 addresses this problem by making intumescent particles from a gel produced from a solution or dispersion of an alkali metal silicate, adding to the gel an oxy boron compound, and then drying and granulating to a convenient particle size. The resulting product retains excellent intumescence even after one hour in boiling water. The product can be produced as caulks and putties by
"mixing uncured polymer binder (e.g., polychloroprene) fillers, resins, and possibly adhesion promoters pigments and solvent (e.g., 50/50 mixture of methyl ethyl ketone and xylene) in a kneader mixer. The intumescent particles would be added during the mixing step. The manufacture of putties is explained in U.S. Pat. No. 4,273,879. Putties are generally more viscous than caulks, having a lower flow rate through a standard (6.4 mm) orifice at 345 kPa, for example less than about 150 grams per minute" (col. 9, lines 41-53). PA1 100 parts of a latex of a halogenated or non-halogenated latex and from 50 to 200 parts of water-insoluble intumescent mineral granules.
Although the product of Graham et al. '333 is not currently available as a caulk, that of Graham '639 is being marketed as a solvent-based caulk. Although solvent based caulks have satisfactory performance, their use has shown to be unpleasant for dwellers in buildings or homes because organic solvent continues to evaporate from the caulk over a period of weeks. The presence of the solvent can cause headaches, nausea or other ailments commonly associated with the inhalation of the solvents.
Another intumescent caulk that uses a volatile organic solvent as a carrier is described in PCT Pat. Publ. No. WO 88/05804 (Miller). The caulk is a composition of a binder such as polyvinyl butyral in a volatile solvent such as trichloroethane, an endothermic filler such as aluminum oxide trihydrate, an exfoliatable (intumescent) mineral such as vermiculite, and preferably also a thixotropic agent such as precipitated silica.
Currently on the market are water-based caulks that are said to be intumescent and fire retardant, e.g., "Metacaulk" from Metalines, Inc. We do not know their compositions, but they are not nearly as intumescent as is the aforementioned caulk made using the Graham '333 granules.